Radiation alarm



1957 M. H. SHAMOS 2,817,768

RADIATION ALARM Filqd Sept. 16, 1954 I ALARM 26% IONIZATION A OR CHAMBER5 INDICATOR el 20 l3 a :3"- 5 Ewe i i a E a 5 7 GONSTANT/ 30 CURRENTDEVICE PHOSPHO 2 g PHOTO TUBE.

30 IT k CURRENT P5 a I I-2 MORRIS usumos INVENTOR 4\'-L'---B-- J- BY m.

vous A I ATTORNEY Unite States F ff f ic i RADIATION ALARM Morris H.Shamos, Riverdaie, N. Y., assignor, by mesne assignments, to Tung-SolElectric Inc., Newark, N. J., a corporation of Delaware ApplicationSeptember 16, 1954, Serial No. 456,442

9 Claims. (Cl. fill-83.6)

This invention relates to radiation alarms and has particular referenceto an alarm system which will sound a warning or produce a visualindication when gamma ray radiation level exceeds a predeterminedtolerance value.

The large increase in the use of radioactive materials during the pastfew years, coupled with the threat of radiation hazards resulting fromatomic warfare make it desirable to have a simple, automatic radiationalarm which will give a signal when the radiation level exceeds apredetermined value. Since such devices should be on duty twenty-fourhours a day it is advisable to use a simple dependable arrangement whichdoes not require a continuous supply of electrical energy in the standbycondition.

The alarms used at present generally consist of ion chambers or Geigercounters coupled to appropriate amplifier circuits to operate presetrelays and alarm systems. In any of these devices hot cathode tubes mustbe used and hence require a continuous supply of heater or filamentcurrent in the standby condition. The level for which these alarms areset is usually the presently accepted tolerance level, which is 6.25milliroentgens per hour.

As used throughout the specification and claims, the term radiationrefers to high frequency electromagnetic energy such as X-rays or gammarays produced by radioactive materials.

One of the objects of this invention is to provide an improved radiationalarm which avoids one or more of the disadvantages and limitations ofprior art arrangements.

' Another object of the invention is to provide a radiation alarm whichconsumes virtually no electrical energy in the standby condition.

Another object of the invention is to increase the sensitivity ofradiation alarms.

Another object of the invention is to provide a radiation alarm whichmay be used to detect neutrons or beta radiation as well as gammaradiation.

One feature of the invention includes an ionization chamber in seriesconnection with a constant current device. A gaseous discharge devicehaving a cold cathode is coupled to this circuit with a relay in serieswith the anode circuit. The relay contacts are connected to an alarmsystem.

Another feature of the invention includes the use of a photoelectrictube in series with a constant current device, the photoelectric tubebeing used in combination with a phosphor which gives off light whenactivated by the radiation which is to be detected.

For a better understanding of the present invention, together with otherand further objects thereof, reference is made to the followingdescription taken in connection with the accompanying drawings.

Fig. l is a schematic diagram of connections showing one arrangement ofthe radiation alarm circuit.

Fig. 2 is a schematic diagram of connections showing an alternatecircuit.

Fig. 3 is a graph which illustrates the operation of the ionizationchamber connected in series with the constant current device.

Referring now to Fig. 1. an ionization chamber 10 includes an envelope11 which is permeable to the radiation to be measured. Inside envelope11 is an anode 12 and a cathode 13. The envelope is filled with anionizable for which the current is reasonably independent of the voltageover a wide range. In series with the ionization chamber is a constantcurrent device 14 which includes an envelope 15 which is opaque to theradiation. The constant current device also includes an anode 16 and acathode l7 and a small quantity of radium salt which provides constantgas ionization. These two circuit elements are connected in series asshown in the figure and are connected to a source of potential 18 whichmay be volts although the circuit can be made to work with a voltagesupply which varies between a hundred and one hundred seventy-fivevolts. In series with the source of potential is a high resistor 20, theuse of which is optional as will be described later when the operationis described. A large capacitor 21 is connected across the potentialsupply and the resistor.

A gaseous discharge device having a cold cathode 23, a control electrode24 and an anode 25 is coupled to the ionization chamber and the constantcurrent device as shown in Fig. l with a relay winding 26 connected inseries with the anode 25 and anode 12. The relay is supplied with a pairof normally open contacts 27 which are connected between the positiveend of the power supply and an alarm or indicator 28, the other side ofwhich is connected to the negative terminal of the power supply andground.

The operation of this circuit is as follows: When the ionization chamberdoes not receive penetrating radiation the resistance between its anodeand cathode is quite high and therefore the voltage drop A across it isquite high while the voltage drop B across the constant current device14 is correspondingly low, thereby maintaining the potential of thecontrol electrode 24 at a value which prohibits conduction through thedischarge device 22 and relay 26 is not operated.

When the radiation is strong enough to produce a current in theionization chamber 10 which is greater than the constant current whichnormally flows through device 14 voltages A and B change abruptly,voltage A dropping to a comparatively low value and voltage .B rising toa value which produces gaseous conduction in tube 22, thereby actuatingthe relay 26, closing contacts 27, and operating the alarm 28. Becauseof the nature of the gaseous discharge device 22 conduction willcontinue until a reset switch 30 is opened and the anode current throughtube 22 is broken. For this reason no holding circuit is required forthe relay. In the circuit diagram in Fig. l capacitor 21 is added to thecircuit in order to supply a large electrical pulse through tube 22 assoon as the tube is tired. This additional power insures the operationof relay 26. After the relay has been operated the normal current frombattery 18 through resistor 20 is strong enough to hold the relayarmature in an operated condition.

There may be some installations where the alarm is required to be shutofl? after an initial operation. This condition may be realized bymaking the capacitor 21 quite large and resistor 20 also quite large sothat the normal flow of current from the battery 18 through the resistoris not suflicient to maintain conduction through the tube 22. Underthese circumstances the tube will be fired when the ionization chamberis made conductive, the relay is operated due to the charge stored incapacitor 21, then the tube is made non-conductive because of the largevoltage drop across resistor 20, and then capacitor Patented Dec. 24,1957 3 21 is slowly charged and the circuit is ready for the detectionof radiation.

The graph shown in Fig- 3 illustrates the voltage division acrosscomponents and. 14.. Curve 1- represents. the current-voltage of. theionization. chamber. 10-

while curve C represents the same characteristic of the constant currentdevice plotted in a reverse manner so that the sum of the voltages isequal to the voltage of battery 18. When the ionization chamber is notirradiated by any penetrating radiation its current is quite low (.ofthe order of 10 ampere or less in the plateau region) and. its currentcharacteristic has the form as indicated by curve 1-1,. the voltageacross component 10 is then illustrated by the distance A while thevoltage across the constant. current device is shown by distance B. Asthe radiation applied to the ionization chamber increases thecharacteristic curves go through the changes indicated by I--2 and 1-3until the predetermined limit is exceeded and the characteristic may berepresented by curve 1-4. It will be evident that as soon as one curvemoves above the other a large change in voltage takes place, the finaldistribution being shown by distances A-' and B.

A somewhat similar circuit has been described and claimed in applicationSerial No. 324,525, filed December 6, 1952, by Morris I-I. Shamos.

It will be obvious that, if gamma rays or X-rays are to be detected, theenvelope 11 must be permeable to such radiation; must have an envelope15 which is opaque to such radiation-: or else the device must beenclosed in a shield which e'liminatesthe action of all outsideradiation.

If alpha, beta, or neutron radiation is to' be detected suitable filtersand envelope material must be provided so that the ionization within theenvelope 11 is proportional to the desired radiation.

Fig; 2 shows the same circuit as Fig. 1 except that the ionizationchamber 16 has been replaced by a photoelectric tube 31 and a phosphor32. The photoelectric tube includes the usual anode 33 and cathode 34and is housed in an enclosure (not shown) which eliminates all visiblelight. The phosphor 32 may comprise any one of the well-knownphosphorescent materials which produce light when activated bypenetrating radiation. It is well-known that the photoelectric tube 31has an operating characteristic Similar to the ionization chamber 10shown by the curves I in Fig. 3. The operation of this device issubstantially the same as the operation described above. In Fig. 2 thecapacitor 21 and resisfor have been omitted to illustrate an alternatecircuit arrangement.

The phosphor 32 may be a trans-stilbene crystal protected from visiblelight by ashield of black paper. In this case gamma radiation andX-ra'ys are detected. 1f the shield is thin enough beta particles willpenetrate the shield, cause fluorescence, and actuate the circuit. Inorder to detect neutrons, a boron containing plastic must be employed,such as polyethylene glycol borate, zinc sulfide compound.

While there have been described and illustrated specific embodiments ofthe invention, it will be obvious that various changes" andmodifications can be made therein without departing from the field ofthe invention which should be limited only by the scope of the appendedclaims.

I claim:

1. A radiation alarm for indicating the presence of penetratingradiation above a predetermined value comprising; a constant currentelectron discharge device including, an anode and a cathode, said deviceresponsive to penetrating radiation; a constant current device in serieswith the electron discharge device and a source of potential; a gaseousdischarge device coupled to the electron discharge device and saidconstant current de- Also the constant current device 14 vice andresponsive to the relative voltage values ap plied thereon; a relayhaving a winding in series with the gaseous discharge device; and analarm means in series with a source of potential and a pair of contactson said relay.

2. A radiation alarm for indicating the presence of penetratingradiation above apredetermined value comprising, an ionization chamberresponsive to penetrating radiation, said chamber passing a constantcurrent in response to a wide range of applied voltages, accomstantcurrent device in series with the ionization chamber and a source ofpotential; a gaseous discharge device coupled. to the constant currentdevice and responsive to the voltage existing thereon, a relay having awinding in series with an electrode insaid gaseous discharge devicc, andan alarm means in series with a source of potential and a pair ofcontacts on said relay.

3. A radiation alarm for indicating the presence of penetratingradiation above a predetermined value com.-

prising, an ionization chamber having an anode and a. cathode, saidchamber arranged to pass current which: is.

proportional to the intensity of the penetrating radiation incidentthereon: but passingv constant current in response to a wide range ofapplied voltages, a constant current device in series with theionization chamber and a source of potential, a gaseous discharge devicecoupled to the constant current device and responsive to the voltageexisting thereon, a relay having a winding in series with an electrodein said gaseous discharge device, and an alarm means in series with asource of potential and a pair of contacts on said relay.

4. A radiation alarm for indicating the presence of penetratingradiation above a predetermined value. com prising; an ionizationchamber having an anode and: a cathode within a permeable envelope; saidchamber arranged to pass current which is proportional to the intensityof the penetrating radiation incident thereon but passing constantcurrent in response to a wide range of applied voltages; a constantcurrent device in series with the ionization chamber and a source ofpotential; said constant currentdevice including an anode, a cathode,and a source of constant ionization within an envelope; a gaseousdischarge device coupled to the constant current device and responsiveto the voltage existing thereon; a relay having a winding in series withan electrode in said gaseous discharge device; and an alarm means inseries with a source of potential and a pairof contacts on said relay.

5. A radiation alarm for indicating the presence of penetratingradiation above a predetermined value comprising; an ionization chamberhaving an anode and a: cathode Within a permeable envelope; said chamberarranged to pass current which is proportional to the intensity of thepenetrating radiation. incident thereon but passing constant current inresponse to a wide range of applied voltages; a constant current devicein series with the ionization chamber and a source of potential; saidconstant current device including an anode, a cathode; an ionizable gas,and a source of constant ionization within an envelope; a gaseousdischarge device coupled to the constant current device and responsiveto the voltage existing thereon; said gaseous discharge devicecomprising an envelope containing an ionizable gas, a cold cathode, acontrol electrode, and an anode; a relay having a winding in seriesconnection between the anode in said gaseous discharge device and asource of potential; and an alarm means in series with a source ofpotential and a pair of contacts on said relay.

6. A radiation alarm for indicating the presence of penetratingradiation above a predetermined value comprising; an ionization chamberhaving an anode andv a cathode within an envelope which is permeable topenetrating radiation; saidv chamber supplied with an external voltageso that the current through the chamber is pro portional to theintensity of the penetrating radiation incident thereon but passingcurrent in response to a wide range of applied voltages; a constantcurrent device including an anode, a cathode, an ionizable gas within anenvelope, and a source of constant ionization, having its anodeconnected to the cathode in the ionization chamber; a gaseous dischargedevice having a cold cathode, an anode, and a control electrode; saidcontrol electrode connected to the cathode of the ionization chamber andthe anode of the constant current device; a source of potential havingits positive terminal connected to the anode in the ionization chamberand its negative terminal connected to the cathode in the constantcurrent device; a relay having a winding in series connection betweenthe anode in said gaseous discharge device and the positive terminal ofsaid source of potential; and an alarm means connected to a pair ofcontacts on said relay.

7. A radiation alarm for indicating the presence of penetratingradiation above a predetermined value comprising, a light sensitivedevice associated with a fluorescent screen which is responsive topenetrating radiation, said device passing constant current in responseto a wide range of applied voltage values, a constant current device inseries with the light sensitive device and a source of potential, agaseous discharge device coupled to the constant current device andresponsive to the voltage existing thereon, a relay having a winding inseries with an electrode in said gaseous discharge device, and an alarmmeans in series with a source of potential and a pair of contacts onsaid relay.

8. A radiation alarm for indicating the presence of penetratingradiation above a predetermined value comprising, a photoelectric cellmounted adjacent to a fluorescent screen which produces light inresponse to penetrating radiation, said photoelectric cell passingconstant current in response to a wide range of applied voltage values,a constant current device in series with the photoelectric cell and asource of potential, a gaseous discharge device coupled to the constantcurrent device and responsive to the voltage existing thereon, a relayhaving a winding in series with an electrode in said gaseous dischargedevice, and an alarm means in series with a source of potential and apair of contacts on said relay.

9. A radiation alarm for indicating the presence of penetratingradiation above a predetermined value comprising; a first dischargedevice which passes current which is proportional to penetratingradiation, the current through said first device being independent ofvoltage changes over a wide range, a second discharge device in serieswith said first device and a source of potential; said second devicealso passing current which is independent of penetrating radiation andvoltage changes over a wide range; a gaseous discharge device connectedto said first and second discharge devices and responsive to therelative voltage values applied thereon, said gaseous discharge deviceincluding a cold cathode, an anode, a con trol electrode, and anionizable gas in an envelope; a relay having a winding Whose terminalsare connected between the anode in the gaseous discharge device and asource of potential; and an alarm means in series with a source ofpotential and a pair of contacts operated by an armature on the relay.

References Cited in the file of this patent UNITED STATES PATENTS2,622,282 Hare Dec. 23, 1952 2,645,722 Chaminade July 14, 1953 2,648,015Greenfield et al Aug. 4, 1953

